The invention pertains to ball bearing-type slides which are typically used to suspend a drawer in a desk, a filing cabinet or the like. More particularly, the invention pertains to slides having at least three slide members wherein the members are sequenced so that under certain conditions there is preferential movement of two slide members relative to a third.
A typical drawer slide has three slide members slidably secured to each other by a number of ball bearings riding in raceways formed on the slide members. For purposes of exposition, the slide member connected to the cabinet or other housing is designated the proximal slide member, the slide member affixed to the drawer is designated the distal slide member and the remaining slide member is designated the intermediate slide member. The drawer is supported by two slide mechanisms, one on either side, which slide mechanisms may be formed as mirror images of each other. When the drawer is in a closed position, the slide members will typically be in a nested configuration. When the drawer is pulled to a fully opened position, the slide mechanism will be in a configuration wherein the intermediate slide member is extended relative to the proximal slide member and the distal slide member is extended relative to the intermediate slide member.
In such basic slide mechanisms, the order in which the intermediate member extends relative to the proximal member and the distal member extends relative to the intermediate member is not necessarily predetermined. Considerations of strength and smoothness of operation may render a given order or sequence preferable in a given slide configuration. Activation of external mechanisms such as drawer locks may require a specific sequence of operation. A three part slide design is shown in U.S. Pat. No. 4,537,450 by Alan R. Baxter which provides sequencing action. That slide relies on two resilient latching members to cooperate in holding the slide members together during extension. A weakness of this design lies in the loss of elasticity of the resilient latch members. Another design of a telescopic rail with locking mechanism is shown in U.S. Pat. No. 5,181,782 by Thadeus H. Wojcik. That slide also relies on resilient fingers on a stop block member and the action of a second locking member. The design still depends upon the resilient nature of the fingers on the stop block and requires two cooperating latching members.
Regardless of the specific sequence, it is desirable that both slide mechanisms extend in the same order. This is so because for a given total extension of the slide mechanism, the strength, or vertical deflection under a given load, may be dependent on the specific relative extensions of the three members. Additionally, if left and right slide mechanisms have not extended in the same order, the drawer will have a tendency to tilt toward the weaker side. It is clear that the sequence upon extension is typically more important than the sequence upon reinsertion because a drawer is used only after extension whereas the reinsertion process is but a transitory one at the end of which both slides are of a necessity in the identical fully nested configuration.
In certain slides, a progression roller is carried by the intermediate member in rolling engagement with the proximal and distal members. This engagement necessitates a simultaneous extension of the intermediate member from the proximal member and the distal member from the intermediate member. Such an arrangement is featured in the Model 4032 drawer slide by Accuride International, Inc. In certain slide configurations, it is desirable that sequencing be provided upon reinsertion so that the distal member is reinserted relative to the intermediate member prior to the intermediate member being reinserted relative to the proximal member. This is particularly desirable in configurations wherein removal of the drawer is accomplished by completely disengaging the distal members from the intermediate members so that the drawer and distal members are removed as a unit. To properly reengage the intermediate and distal members it is thus desirable that the sequencing mechanism hold the intermediate members fully extended from the proximal members until the re-engagement has occurred. Once such slide which uses a rotating latch is disclosed in U.S. Pat. No. 4,560,212 by John E. Papp and Antony S. Reed.